IP Over Satellite

© 2009 N. N. Maurya© 2009 N. N. Maurya
IP Over Satellite
N. N. Maurya

© 2009 N. N. Maurya
IP via Satellite
 Achieved by interfacing satellite modems directly to IP routers
 via channel serial router interfaces
• G703: 2Mbit/s
• RS449/422 up to 8Mbit/s and HSSI up to 52Mbit/s
 using serial encapsulation link layer protocols (e.g. Frame Relay)
 Maximizes satellite broadcast capabilities

IP Distributions
 xDSL
 Digital Cable
 Optical Fiber
 WiMax
 3G
 Satellite – Why ?

IP Over Satellite – Why ?
 Global coverage
 In air, in water and in remote solution
 Easy deployments, maintenance, upgradation
 Anywhere, everywhere

Satellite IP networks
 Protocol-centric viewpoint of satellite
IP network
 Satellite-centric viewpoint of global
networks and the Internet
 Network-centric viewpoint of satellite
networks

Satellite IP networks: Protocol-centric
 Emphasizes the protocol stack and protocol functions
 IP provides a uniform network hiding away all differences
between different technologies
 Different networks may transport IP packets in different
ways
Relationship between IP and different network technologies

Satellite IP networks: Satellite-centric
 Emphasizes the satellite network itself
 GEO or non-GEO
 MEO
 LEO

Satellite IP networks: Network-centric
 Emphasizes networking functions rather than
satellite technologies
 Satellite systems and technologies concern two
aspects: the ground segment and the space segment
 In the space segment, various types of technology can
be used including transparent (bent-pipe)
transponder, on-board processor, on-board circuit
switch, on-board packet switch, on-board DVB-S or
DVB-RCS switch or IP router
 Regenerate transponder

Satellite IP networks: Network-centric
 Future satellites with on-board DVB switching will be
able to integrate broadcast and interactive services
by combining DVB-S and DVB-RCS standards.
 A DVB-S regenerative payload can multiplex
information from diverse sources into a standard
downlink DVB-S stream
 Another example of the use of DVB on-board
switching is to interconnect LANs using IP over
MPEG-2 encapsulation, via a regenerative satellite
payload

IP packet encapsulation:
IP over satellite
 Satellite networks need to provide a frame structure
so that the IP datagram can be encapsulated into the
frame and transported via satellite from one access
point to other access points
 ATM networks use ATM adaptation layer type 5
(AAL5) to encapsulate IP packets for transmission
over the ATM network
 In DVB-S, IP packets including multicast are
encapsulated in an Ethernet-style header using a
standard called multi-protocol encapsulation (MPE)

Satellite IP networking
 Global coverage (including land, sea and air), efficient
delivery to a large number of users on a large scale,
and the low marginal cost of adding additional users
 A satellite can play several different roles in the
Internet:
 Last mile connections
 Transit connections
 First mile connections

 Last mile connections
 User terminals directly access the satellite, which provides
direct forward and return links
 Traffic sources connect to the satellite feeder or hub
stations through the Internet, tunnelling or dial-up links
 It is the last mile to reach user terminals

 Transit connections
 Satellite provides connections between Internet gateways or
ISP gateways.
 The traffic is routed through the satellite links according to
specified routing protocols and defined link metrics in the
networks so as to minimise connection costs and to meet
required QoS constraints for the given traffic sources

 First mile connections
 Satellite provides forward and return link connections
directly to a large number of ISPs.
 IP packets start from the servers as the first mile of their
journey to user terminals.
 Server connect to the satellite feeder or hub stations
directly or through the Internet tunnelling or dial-up links

Routing on board satellites
 The benefit of an IP router in the sky is that it allows
satellite networks to be integrated into the global
Internet using the standard routing algorithms
 With a constellation, there are many satellites
forming a subnet to cover the earth. Therefore,
routing within the constellation satellite network is
required.

IP mobility in satellite networks
 For a network with a constellation of LEO satellites
the relationships between the satellite network and
user terminals are changing continuously.
 Therefore, there are several issues concerned with
mobility:
 Re-establishing the physical connections with the satellite
networks.
 Timely updating the routing table so that IP packets can be
routed to the right destination.
 Mobility within the satellite networks.
 Mobility between terrestrial networks and satellite
networks.

IP over Satellite (IPoS)
Global Standard
 IPoS Standard Approvals
 TIA Standard 1008, November 2003
 ETSI Standard TS102354, TSS-B, January
2005 (ITU Approved)
 Advantages
 Optimized transponders
 Extends DVB-S with alternative uplink
architecture
 Scalable and economical
 Extendable to Ka- and C-band
 It utilizes a technology called DVB-S2 and
supports data throughputs of up to 120
Mbps.
Physical Layer
Data Link Control Layer
Network Adaptation Layer
Network Adaptation
Satellite Dependent
Satellite Independent
SI-SAP
Telecommunication Industry Association (TIA)

IPoS Architecture

IPoS System Architecture

Orbital Options
 A Geosynchronous satellite (GEO) completes
one revolution around the world every 23 hrs
and 56 minutes in order to maintain continuous
positioning above the earth’s sub-satellite point
on the equator.
 A medium earth orbit satellite (MEO) requires
a constellation of 10 to 18 satellites in order to
maintain constant coverage of the earth.
 A low earth orbit satellite (LEO) offers
reduced signal loss since these satellites are 20
to 40 times closer to the earth in their orbits
thus allowing for smaller user
terminals/antennas.

Geostationary Orbit
(GEO)
Characteristics of Geostationary (GEO) Orbit Systems
• User terminals do not have to track the satellite
• Only a few satellites can provide global coverage
• Maximum life-time (15 years or more)
• Above Van Allen Belt Radiation
• Often the lowest cost system and simplest in terms of tracking and high speed
switching
Challenges of Geostationary (GEO) Orbit
• Transmission latency or delay of 250 millisecond to complete up/down link
• Satellite antennas must be of larger aperture size to concentrate power and to
create narrower beams for frequency reuse
• Poor look angle elevations at higher latitudes

Geostationary Orbit Today

Low Earth Orbit (LEO)
Characteristics of Low-Earth Orbit (LEO) Systems
- Low latency or transmission delay
- Higher look angle (especially in high-latitude regions)
- Less path loss or beam spreading
- Easier to achieve high levels of frequency re-use
- Easier to operate to low-power/low-gain ground antennas
Challenges of Low-Earth Orbit (LEO) Systems
- Larger number of satellites (50 to 70 satellites). Thus higher
launch costs to deploy, build, and operate.
- Harder to deploy, track and operate.
- Shorter in-orbit lifetime due to orbital degradation

Medium Earth Orbit
(MEO)
Characteristics of Medium-Earth Orbit (MEO) Systems
• Less latency and delay than GEO (but greater than LEO)
• Improved look angle to ground receivers in higher latitudes
• Fewer satellites to deploy and operate, cheaper systems than LEO
(but more expensive than with GEO)
• Longer in-orbit lifetime than LEO systems (but less than GEO)
Challenges of Medium-Earth Orbit (MEO) Systems
• More satellites to deploy than GEO (10 to 18 vs. 3 to 4)
• Ground antennas are generally more expensive and complex
because of the need to track satellites.

IP multicast over satellite
 Satellite networks can be part of an IP multicast
routing tree at the source, trunk or end branch
forwarding IP packets towards their destination.

IP Unicast
Wastes network bandwidth

IP Unicast
 Wastes network bandwidth
 Recipients provide feedback, so the sender
can find out what to retransmit.
 This is known as automatic repeat request
(ARQ) mechanism

IP Multicasting
 IP Multicast
 Types
 IGMP
 Network-layer multicast algorithms
 Multicast routing

IP Multicast
 Unicast : one copy for EACH receiver
 Multicast : one copy for ALL receivers
 Efficient : One-to-Many Data Distribution
Unicast Multicast
Source
Receiver 1 Receiver 2 Receiver 1 Receiver 2
Source
Router Router

IP Multicast

IP Multicast
 In multicast, classical ARQ may not be
always the most appropriate solution.
 Forward error correction (FEC) codes
are a great tool for improving the
efficiency of error recovery in
multicast communications.

Error Control Mechanisms
for Multicast
 Reliable protocols provide a mechanism to ensure that data is
properly received by every intended destination.
 Unreliable protocols only perform best-effort delivery and have
no mechanism for recovery from failures in transmission.
 Streaming applications, like real-time audio and video, can
tolerate occasional loss of packets - unreliable multicast is
unacceptable.
 A reliable protocol needs to be able to perform loss recovery.
 automatic repeat request (ARQ) and forward error correction
(FEC)
 A combination of the two is known as hybrid ARQ (HARQ)

IP Multicast - Types
 Multicast can be either best effort or reliable.
 ‘Best effort’ means that there is no mechanism to
guarantee that the data sent by any multicast source
is received by all or any receivers, and is usually
implemented by a source transmitting UDP packets on
a multicast address.
 ‘Reliable’ means that mechanisms are implemented to
ensure that all receivers of a multicast transmission
receive all the data that is sent by a source: this
requires a reliable multicast protocol.

Advantages of multicast
 Reduced network bandwidth usage
 Reduced source processing load

IP multicast addressing
 Each terminal or host in the Internet is uniquely identified
by its IP address.
 In IPv4, an IP address has 32 bits, divided into a network
number and a host number, which respectively identify a
network and the terminal attached to the network
 A normal unicast IP datagram includes a source address
and destination address in the IP packet header; routers
use the destination address to route the packet from the
source to the destination
 Such a mechanism cannot be used for multicast purposes,
since the source terminal may not know when, where and
which user will try to receive the packet

IP multicast addressing …
 A range of addresses is set aside for multicast purposes
only
 The range of addresses, called Class D addresses, is from
224.0.0.0 to 239.255.255.255
 Unlike Classes A, B and C, these addresses are not
associated with any host number, but instead are
associated with a multicast group, like a radio channel
 Members of the group receive multicast packets sent to
this address, and the address is used by multicast routers
to route IP multicast packets to users that register for a
multicast group.
 The mechanism by which a terminal registers for a group
is IGMP.

Multicast group management
 The Internet group membership protocol (IGMP) allows
hosts or terminals to declare an interest in receiving a
multicast transmission
 IGMP supports three main types of message: report, query
and leave
 A terminal wishing to receive a multicast transmission
issues an IGMP join report, which is received by the
nearest router.
 This report specifies the IP multicast Class D
address of the group being joined.
 The router then uses a multicast routing protocol to
determine a path to the source.

Multicast group management
 When a terminal wishes to finish receiving the
multicast transmission it issues an IGMP leave
request
 The leave message is supported in IGMP Version 2

IP multicast routing
 Multicast routing protocols address the issue of
identifying a route for data to be transmitted across
a network from a source to all its destinations, while
minimising the total network resources required for
this.
 In IP multicast, the routing table is effectively built
from destinations to the sources rather than from
sources to destinations
 Tunnelling techniques may also be used to support
multicast over routers that do not have multicast
capabilities

Multicast routing protocols
 Distance vector multicast routing
protocol (DVMRP)
 Protocol-independent multicast-sparse
mode (PIM-SM)
 PIM dense mode (PIM-DM)
 Core-based tree (CBT)

DVMRP and PIM-DM
 DVMRP and PIM-DM uses ‘flood and prune’ algorithms
 When a source starts sending data, the protocols
flood the network with the data
 All routers that have no multicast recipients attached
send a prune message back towards the source
 These protocols have the disadvantage that a ‘prune’
state is required in all routers, including those
routers with no multicast recipients downstream
 Flood and prune protocols use reverse path
forwarding (RPF) to forward multicast packets from a
source to the recipients

DVMRP and PIM-DM …
 The RPF interface for any packet is the interface that the
router would use to send unicast packets to the packet
source
 If a packet arrives on the RPF interface it is flooded to all
other interfaces, but if the packet arrives on any other
interface it is silently discarded.
 This ensures efficient flooding and prevents packet
looping.

DVMRP and PIM-DM …
 DVMRP uses its own routing table to compute the
best path to the source, whereas PIM-DM uses an
underlying unicast routing protocol

IP multicast scope
 Scoping is the mechanism that controls the
geographical scale of a multicast transmission, by
making use of the time to live (TTL) field in the IP
header.
 It tells the network how far (in terms of router hops)
any IP packet is allowed to propagate, allowing IP
multicast sources to specify whether packets should
be sent only to the local subnetwork, or to larger
domains or the whole Internet.
 This is achieved by each router reducing the TTL by 1
whenforwarding the packet to the next hop, and
discarding the packet if the TTL is 0.

IP multicast scope …
 In a satellite network even with a small TTL value, IP
multicast packets can reach a very large number of
members of a multicast group scattered over a very
large geographical area

IGMP behaviour in satellite
environments
 IGMP over satellites raises interoperability issues
 In a conventional terrestrial LAN, an IGMP report is
heard by other multicast receivers on the LAN, and
this prevents flooding of the LAN with multiple
reports
 In a satellite system, individual ground stations
cannot hear each other; given the large number of
multicast receivers that are expected in satellite
systems (potentially of the order of 105 or 106)
multiple IGMP reports could cause significant
flooding of the satellite network with IGMP traffic

IGMP behaviour in satellite
environments …
 One of a number of adaptations of IGMP and
multicast must therefore be implemented
 Two options:

Multicast routing protocols in
a satellite environment

IGMP adaptation over
satellite

Thank You

IP Over Satellite

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